hosts file

A text file on a networked computer used to
associate host names with IP addresses. A hosts file
contains lines consisting of whitespace-separated fields
giving an IP address followed by list of host names or
aliases associated with that address. The name resolution
library software can use this file to look up the IP address
for a host name. The hosts file is "/etc/hosts" on Unix and
"C:\Windows\System32\drivers\etc\hosts" or "lmhosts" on
Microsoft Windows,

In most cases, hosts files have now been almost entirely
replaced by DNS, in which distributed servers provide the
same information. A hosts file can still be used to override
DNS for testing purposes or other special situations.